The present invention relates to a digital component video signal processor in a system for recording, reproducing or transmitting a digitized component video signal, for example, a system such as a digital VTR.
A digital VTR for component video signal or a so-called D-1 VTR was put into practice commercially several years ago. The D-1 VTR is a digital VTR in which a 4:2:2 signal shown by the CCIR recommendation 601 is recorded or reproduced in a form quantized into 8 bits. The 4:2:2 signal is a signal obtained by sampling a luminance signal and two color-difference signals at 13.5 MHz and 6.75 MHz, respectively, and this 4:2:2 signal is conformable to the existing television signal which has an aspect ratio of 4:3 and is based on a scanning system of 525 lines per 60 Hz and 625 lines per 50 Hz. On the other hand, there is a trend toward an aspect ratio of 16:9 or a further lateral extension with the scanning system being kept as it is. Such a television system is called EDTV-II in Japan, ATV in U.S.A., and clean PAL, PAL plus or extended 4:2:2 in Europe. In the present specification, it will be called the extended 4:2:2 system.
If the sampling frequency of the extended 4:2:2 system is selected to be (16/9)/(4/3)=4/3 times as high as that of the normal 4:2:2 system, it is convenient since a horizontal resolution the same as that in the normal 4:2:2 system is obtained even if the further lateral extension is made. In this case, the sampling frequencies of a luminance signal and two color-difference signals are 18 MHz and 9 MHz, respectively. Provided that a signal obtained by quantizing those signals into 8 bits is a first digital component video signal, the data rate of that signal in a word rate frequency and bit rate representation is as follows: EQU word rate frequency: 18+9.times.2=36 MHz EQU bit rate: (18+9.times.2).times.8=288 Mbits/sec.
On the other hand, the data rate of the D-1 VTR is as follows: EQU word rate frequency: 13.5+6.75.times.2=27 MHz EQU bit rate: (13.5+6.75.times.2).times.8=216 Mbits/sec.
The details of the conventional digital VTR have been disclosed by, for example, SMPTE D-1 DTTR (SMPTE Journal, December, 1986). The prior art method of encoding a 10-bit sample or word into a 8-bit word, which is used in embodiments of the present invention, has been disclosed by U.S. Pat. No. 4,730,223.
Now consider D-X as a digital VTR for recording/reproducing the above first digital component video signal. The bit rate of the D-X VTR is increased to 288/216=113% as compared with that of the D-1 VTR. Therefore, it is not possible to use the conventional D-1 VTR as the D-X VTR, and hence it is necessary to develop a novel digital VTR as the D-X VTR. However, since the 4:2:2 signal corresponding to the existing television signal having an aspect ratio of 4:3 will be used even in the future, the D-1 VTR will also be necessary even if a new digital VTR is fabricated as D-X. In that case, there will be two kinds of digital VTR's and casettes for D-1 and D-X, which is troublesome.